The objectives of this project lie in two major areas. The first is to continue our studies of the natural history of avian leukosis, to clarify the relationships between contact and congenital transmission, to analyze the status of avian leukosis virus (ALV) in nonviremic progeny of viremic hens, and to investigate long term chronic effects of persistent tolerant infection with ALV. The second major objective is isolation and purification of individual group-specific antigens of ALV, to correlate these with viral sub-structure and with related gs antigens and particles in host tissues.